This invention relates to a continuous process for producing spinnable polyester polymers. More specifically, this invention relates to a continuous process for producing spinnable polyester polymers wherein solid polymer additives are added to the process stream at a point where the polymer is molten. In one preferred embodiment, the invention relates to a process for preparing an improved heat stable polyester polymer by late addition of a copper complex compound to the polymer.
Linear high-molecular weight polyethylene terephthalate film and fiber forming polyesters are well known. They are prepared commercially either by the ester interchange reaction between dimethyl terephthalate and a glycol or by the direct esterification process wherein terephthalic acid is reacted directly with ethylene glycol. These products and processes are well documented in U.S. Pat. Nos. such as 2,465,310; 3,050,533; 3,051,212; 3,427,287 and 3,484,410, which cover not only the basic products and processes but many improvements thereon. And though many improvements naturally have evolved from such a highly successful commercial product, such success generates more and more uses and such new uses as well as old ones create demands for a better product in today's commercial arena of positive competition.
Polyethylene terephthalate fibers and cords are known to exhibit excellent dimensional stability, that is, low extension or growth during service, as well as to have a high resistance to thermal degradation; however, in tires under high speed conditions under heavy load, loss of tensile strength is experienced due to high temperature conditions emanating under such conditions. The following patents are particularly pertinent to this problem:
U.S. Pat. No. 3,563,848 to R. S. Bhakuni et al. relates to the production of thermally stabilized polyesters. More particularly, this patent discloses an improved rubber structure reinforced with a polyester fiber modified with either a metal complex alone or in combination with a polycarbonate alone or in combination with an isocyanate, the modifier being present in the polyester prior to fiber formation.
More recently, U.S. Pat. No. 3,833,542 to S. D. Lazarus et al. discloses an improved high molecular weight linear polyester having a small amount of dichloro(di-2-pyridylamine) copper (II) or bis(di-2-pyridylamine) copper (II) chloride incorporated therein to improve thermal stability. This patent suggests late addition of the metal complex to the molten polymer in a continuous process; however, the liquid carrier for the metal complex, tris(nonyl phenyl)phosphite, is not very satisfactory because it causes the polymer to become gray in color.
Although these patents constitute an important contribution to the art, research in this field has continued, particularly with respect to continuous injection of solid additives into molten polyester. Those skilled in this art know that in conventional polymer chip spinning processes, it is possible to coat the chips with a polymer additive. However, this method cannot be used in a continuous process wherein polycondensation is followed directly be spinning of the molten polymer. Accordingly, the present invention is directed primarily to providing an improved continuous process for production of polyester polymers wherein the polymer additives are added to the process stream at a point where the polymer is molten, whereby the resultant molten polymer can then be used directly in the preparation of shaped articles, particularly fibers.